IEEE Electrification Magazine - June 2015 - 25

Navies around the
world have been
actively exploring
integrated power
systems for use on
future surface
combatant ships
since the late
20th century.

common couplings (PCCs) of the grid,
are physically separated to each other
as well as their own tie circuit breakers to enhance the chances of survival. There are two propulsion systems
for redundancy and survivability. Furthermore, half of the propulsion
power is provided by its own switchboard and the other half by the opposite bus for cross-feeding, which is
not described in Figure 2. Therefore,
even if one switchboard fails for any
reason, continuous power can be provided to the propulsion motors.
However, this type of reliability is a
hindrance for fuel economy. The
engine generators run for reliability
seldom result in efficient operation points, which usually
lie above the medium load. This tradeoff between reliability and fuel economy becomes more complicated as the
naval surface ship operates in various speeds and the
electric loads vary independently. The minimum generator operation (MGO) with N-1 safety (contingency) can be
considered as a simple solution and, further, as a standard operation rule to this tradeoff. This rule is based on
the idea that the less the generators are run, the more

load is on each generator. This, in
turn, makes the operation more efficient. However, the predetermined
system components and operation
status mean that there is not much
room for improvement.
Adopting an onboard BESS provides
an opportunity for improvement. The
BESS can be seen as an additional
degree of freedom in the system
design. Hence, the fuel efficiency can
be increased while guaranteeing reliability. When one online generator suddenly stops for any reason, the BESS
can cover the active power shortage for
a while to keep the power grid continuously maintained like an extra generator until another generator on standby is synchronized
according to N-1 safety. Therefore, the BESS can change the
operation strategy of the engine generator to become more
efficient without sacrificing reliability.

Design Procedure of the Onboard
BeSS Power Capacity
The power capacity and energy of the onboard BESS
should be determined according to MGO and N-1 safety.

Main Grid
(PCC)
#1 Main Switchboard
Power Generation
System
Generator

Electric Propulsion System (Starboard)
M

Prime
Mover

CircuitBreaker
#1 Generator Set
Generator
Prime
Mover

#1 Load Center

Ship Service Load System
Ship Service Loads
(Nonvital Loads)

#1 Ship Service
Transformer

Ship Service Loads
(Vital Loads)

#3 Generator Set
#2 Main
Switchboard

Bus Tie

Bus Tie
#2 Load Center

Automatic
Bus Transfer

Generator
Prime
Mover

#2 Ship Service
Transformer
Ship Service Loads
(Nonvital Loads)

#2 Generator Set
Generator
Prime
Mover

#4 Generator Set
Electric Propulsion System (Port)
Figure 2. A typical IPS of a naval ship model (small and medium class).

IEEE Electrific ation Magazine / j une 2 0 1 5

Table of Contents for the Digital Edition of IEEE Electrification Magazine - June 2015